Yes, pool algae can be brown. This typically indicates mustard algae (yellow-brown) or dead/dying green algae that has turned brownish. Treatment requires proper identification and targeted chlorine shock treatment.
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Yes, pool algae can absolutely be brown. Brown coloration in pool water typically indicates either mustard algae (which appears yellow-brown), dead or dying green algae that has oxidized to a brownish color, or in rare cases, true brown algae. The brown appearance often confuses pool owners who expect algae to always be green, but proper identification and treatment will restore your pool to crystal clear condition.
The most common cause of brown algae appearance is actually mustard algae, scientifically known as yellow algae. This stubborn organism appears yellow-brown to brownish-green and typically clings to pool walls, steps, and shaded areas. Mustard algae is chlorine-resistant and often mistaken for dirt or sand because it brushes off easily but returns quickly.
Mustard algae thrives in pools with inadequate chlorine levels relative to stabilizer (CYA) levels. It's particularly common in warmer climates and can survive in properly chlorinated water if the free chlorine to CYA ratio isn't maintained correctly.
Green algae that has been shocked with chlorine often turns brown or grayish-brown as it dies and oxidizes. This is actually a good sign that your shock treatment is working, but the dead algae needs to be filtered out completely to prevent it from becoming food for new algae growth.
True brown algae is relatively rare in swimming pools but can occur, particularly in pools with high organic content or those that have been neglected for extended periods. This type appears as a brownish film or coating and is often accompanied by other contaminants.
Examine the algae's behavior and appearance closely. Mustard algae typically appears in patches on pool surfaces, especially in areas with less circulation. It brushes off easily with a pool brush but returns within 12-24 hours. True brown algae tends to form more of a coating or film.
Use a pool brush to disturb the brown material. If it creates a cloud that settles back down, you're likely dealing with mustard algae. If it comes off in sheets or films, it might be true brown algae or biofilm.
Test your water chemistry immediately using a quality test kit like the Taylor K-2006C. Focus on free chlorine (FC), combined chlorine (CC), pH, total alkalinity (TA), and cyanuric acid (CYA) levels. Brown algae problems often correlate with improper FC/CYA ratios.
Before adding any chemicals, get accurate readings of all chemical levels. For mustard algae treatment, you'll need to follow a modified SLAM (Shock Level And Maintain) process that's more aggressive than standard green algae treatment.
Brush all pool surfaces vigorously, paying special attention to areas where brown algae is visible. This step is crucial because mustard algae clings tightly to surfaces and must be disturbed to expose it to sanitizer.
For mustard algae, raise free chlorine to shock level based on your CYA reading, then add an additional 10 ppm. If your CYA is 50 ppm, normal shock level would be 20 ppm FC, but for mustard algae, target 30 ppm FC. Use liquid chlorine (sodium hypochlorite) rather than calcium hypochlorite to avoid raising calcium hardness.
Dosing calculation: Each gallon of 12.5% liquid chlorine raises FC by approximately 13 ppm in 10,000 gallons of water. Adjust accordingly for your pool size.
Unlike green algae treatment, mustard algae requires maintaining shock level for 24-48 hours minimum. Test FC every 8 hours and add more liquid chlorine to maintain your target level. The algae must be completely eliminated before reducing chlorine levels.
Liquid chlorine will raise pH, so monitor and adjust using muriatic acid to keep pH between 7.4-7.6. High pH reduces chlorine effectiveness, making algae harder to kill.
Run your pool pump and filter 24/7 during treatment. Mustard algae and dead brown algae particles must be filtered out completely. Backwash or clean your filter when pressure rises 8-10 psi above starting pressure.
Mustard algae can survive on pool equipment and toys. Soak all pool accessories, including brushes, vacuum heads, and toys, in a solution of 10% liquid chlorine for several hours or overnight.
For persistent mustard algae, consider using a filter cleaner like Natural Chemistry Filter Perfect or soaking filter elements in a mild muriatic acid solution (1 part acid to 20 parts water) to remove algae residue.
The key to preventing brown algae is maintaining adequate free chlorine relative to your stabilizer level. Use the FC/CYA chart: for 50 ppm CYA, maintain minimum 4 ppm FC daily, with 6 ppm preferred for mustard algae prevention.
Brush your pool weekly, focusing on areas with poor circulation. This prevents algae from establishing colonies on surfaces.
In areas prone to mustard algae, shock weekly to break chloramines and eliminate developing algae colonies before they become visible.
If brown algae persists after 72 hours of proper SLAM treatment, or if you're uncomfortable handling large quantities of liquid chlorine, contact a certified pool professional. Some cases may require specialized algaecides or equipment cleaning that's best handled professionally.
Remember, successful brown algae treatment requires patience and consistent chemical maintenance. The key is identifying the specific type of algae and following through with complete treatment rather than taking shortcuts that allow the problem to return.
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